Advice on this ranges from weekly to whenever it looks dirty, and the honest answer depends on which layer you mean. Different items accumulate very different amounts of what makes bedding dirty.
What Accumulates
Sweat, which is substantial across a night. Skin cells, which are shed continuously and are what dust mites feed on. Body oils, which transfer readily to fabric. Hair and hair products. And whatever comes in on skin from the day.
The layers closest to the body receive nearly all of this, which is why the recommended frequency varies so much between items.
The Flat Sheet Changes the Answer
A flat sheet between the sleeper and the duvet takes most of the sweat and oil, which means the duvet cover needs washing considerably less often.
This is the practical argument for a layer many households have abandoned. Washing one lightweight sheet weekly is easier than washing a full duvet cover at the same frequency.
The same logic applies to a quilt used over a duvet: the washable top layer protects the layer that is harder to clean. Ranges built around machine-washable quilts and coverlets, such as those at han-sleep.com, suit that arrangement.
Reasonable Intervals
- Pillowcases and sheets: weekly, or more often in hot weather
- Pillow protectors: every few weeks
- Quilts and coverlets used as the top layer: every few weeks to monthly
- Duvet covers: every two to three weeks if a flat sheet is used, weekly if not
- The duvet itself: once or twice a year
- Pillows: two or three times a year, where washable
- Mattress protector: every couple of months
When to Wash More Often
Hot weather, illness, sharing a bed with a pet, sweating heavily, eating in bed, or any skin condition where cleanliness matters.
Anyone with a dust mite allergy is generally advised to wash bedding weekly at a temperature high enough to kill mites, which is considerably hotter than a normal wash. This is one of the few cases where a hot wash is genuinely warranted.
Pillows Get Forgotten
Pillows absorb a great deal and are washed rarely. Many synthetic pillows are machine washable; down and feather frequently are not without care.
Pillow protectors under the case are the practical answer, since they can be washed easily and substantially extend how long the pillow stays acceptable.
The Realistic Standard
Weekly for sheets and pillowcases is the guideline most sources converge on, and fortnightly is what a large proportion of households actually manage.
Having two sets and rotating them is what makes weekly achievable, because the bed can be remade immediately rather than waiting for a wash to finish.
Airing
Pulling bedding back rather than making the bed immediately lets moisture evaporate rather than being trapped. It takes no effort and reduces the humidity that dust mites depend on.